From JWF:

Anyone surfing the web recently has no doubt come across this ravishing creature looking back at you. Thanks to a commenter over at AoS, we now know who she is.  Melissa Theuriau owns the ubiquitous face of countless web advertisements.

She is a French journalist and news anchor.  According to wikipedia:
Mélissa Theuriau has become an internet phenomenon, with fans uploading video compilations receiving millions of hits from admirers. Theuriau is reportedly surprised by this phenomenon, stating, “I cannot explain it…I am absolutely not seeking this publicity.”

I am considering moving to France just so I can watch her do the news every day.

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